The invention relates generally to an electrophysiological (xe2x80x9cEPxe2x80x9d) apparatus and method for providing energy to biological tissue, and more particularly, to a steerable catheter with a preformed distal shape and a movable outer sleeve for positioning the catheter to a desired location in a patient.
The heart beat in a healthy human is controlled by the sinoatrial node (xe2x80x9cS-A nodexe2x80x9d) located in the wall of the right atrium. The S-A node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (xe2x80x9cA-V nodexe2x80x9d) which in turn transmits the electrical signals throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth of, or damage to, the conductive tissue in the heart can interfere with the passage of regular electrical signals from the S-A and A-V nodes. Electrical signal irregularities resulting from such interference can disturb the normal rhythm of the heart and cause an abnormal rhythmic condition referred to as xe2x80x9ccardiac arrhythmia.xe2x80x9d
While there are different treatments for cardiac arrhythmia, including the application of anti-arrhythmia drugs, in many cases ablation of the damaged tissue can restore the correct operation of the heart. Such ablation can be performed by percutaneous ablation, a procedure in which a catheter is percutaneously introduced into the patient and directed through an artery or vein to the atrium or ventricle of the heart to perform single or multiple diagnostic, therapeutic, and/or surgical procedures. In such case, an ablation procedure is used to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities or create a conductive tissue block to restore normal heart beat or at least an improved heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels. A widely accepted treatment for arrhythmia involves the application of RF energy to the conductive tissue.
In the case of a trial fibrillation (xe2x80x9cAFxe2x80x9d), a procedure published by Cox et al. and known as the xe2x80x9cMaze procedurexe2x80x9d involves continuous atrial incisions to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium. While this procedure has been found to be successful, it involves an intensely invasive approach. It is more desirable to accomplish the same result as the Maze procedure by use of a less invasive approach, such as through the use of an appropriate EP catheter system.
There are two general methods of applying RF energy to cardiac tissue, unipolar and bipolar. In the unipolar method a large surface area electrode; e.g., a backplate, is placed on the chest, back or other external location of the patient to serve as a return. The backplate completes an electrical circuit with one or more electrodes that are introduced into the heart, usually via a catheter, and placed in intimate contact with the aberrant conductive tissue. In the bipolar method, electrodes introduced into the heart have different potentials and complete an electrical circuit between themselves. In the bipolar method, the flux traveling between the two electrodes of the catheter enters the tissue to cause ablation.
During ablation, the electrodes are placed in intimate contact with the target endocardial tissue. RF energy is applied to the electrodes to raise the temperature of the target tissue to a non-viable state. In general, the temperature boundary between viable and non-viable tissue is approximately 48xc2x0 Centigrade. Tissue heated to a temperature above 48xc2x0 C. becomes non-viable and defines the ablation volume. The objective is to elevate the tissue temperature, which is generally at 37xc2x0 C., fairly uniformly to an ablation temperature above 48xc2x0 C., while keeping both the temperature at the tissue surface and the temperature of the electrode below 100xc2x0 C.
Failure to bring or maintain the electrodes in contact with the target tissue may result in the RF energy not reaching the tissue in sufficient quantities to effect ablation. Only limited electromagnetic flux in a bipolar approach may reach the tissue when the electrode is non-contacting. In a unipolar approach, the RF energy may spread out too much from the non-contacting electrode before reaching the tissue so that a larger surface area is impacted by the flux resulting in each unit volume of tissue receiving that much less energy. In both cases, the process of raising the tissue temperature to the ablation point may require a much greater time period, if it can be performed at all. Where the electrodes have temperature sensors and those sensors are not in contact with the tissue, they may not sense the actual temperature of the tissue as fluids flowing around the non-contacting electrode may lower the temperature of the electrode and the temperature sensed by the sensors.
In the treatment of atrial fibrillation, a plurality of spaced apart electrodes are located at the distal end of a catheter in a linear array. RF energy is applied to the electrodes to produce a long linear lesion. With such a linear array, intimate contact between each electrode and the target endocardial tissue is more difficult to maintain in the heart due to the irregular heart surface contours and the constant movement of the heart. The lesion produced may have discontinuities unless steps are taken to maintain contact. These lesions may not be sufficient to stop the irregular signal pathways and arrhythmia may reoccur. Thus the need for catheters having the capability to conform to and maintain intimate contact with various endocardial tissue surface contours is strongly felt by those engaged in the treatment of cardiac arrhythmias, particularly atrial fibrillation.
To that end, several catheter systems have been developed in an attempt to ensure intimate contact between the electrodes at the distal end of a catheter and the target tissue. In one such catheter system, described in U.S. Pat. No. 5,617,854 to Munsif, the distal end of the catheter is shaped to conform to a specific region of the heart. The catheter is made of a shaped-memory material, e.g. nitinol, and formed in a specific shape. During use, the catheter is deformed and introduced through an introducer sheath to the heart where ablation is to occur. Once in position, the sheath is retracted and the catheter is reformed into its specific shape when heated to body temperature or when a current is passed through the shaped-memory material. If the shaped memory of the catheter matches the curvature of the biological cavity, there is more intimate contact between the electrode and the tissue and a more continuous lesion is formed. If a given shaped catheter does not conform to the shape of the biological site to be ablated a different catheter having a different preformed shape must be used. Requiring a collection of preformed-shaped catheters, as such, is economically inefficient.
In another catheter system, described in U.S. Pat. No. 5,882,346, to Pomeranz et al., the catheter system includes a catheter having a lumen extending through it and a plurality of electrodes at the distal-end region. A core wire is insertable into the catheter lumen. The core wire includes a preshaped region that is formed of a superelastic material and which is bent into a predetermined shape. As the core wire is inserted into the catheter, the core wire deforms the distal-end region of the catheter into the predetermined shape of the core wire. If the predetermined shape of the core wire matches the curvature of the biological cavity, there is more intimate contact between the electrodes and the tissue. If, however, a given preshaped core wire does not conform to the shape of the biological site to be ablated a different core wire having a different preformed shape must be used. Thus a collection of different shaped core wires is required. This is also economically inefficient.
Hence, those skilled in the art have recognized a need for providing a single catheter carrying a plurality of electrodes in its distal-end region which is capable of conforming to various curvatures of the biological site so that intimate contact may be maintained between the electrodes and the site. The invention fulfills these needs and others.
Briefly, and in general terms, the invention is related to an apparatus and a method for use in applying energy to a biological site using a catheter carrying at least one electrode in its distal-end region which is capable of conforming to various curvatures of the biological site so that intimate contact may be maintained between the electrodes and the site.
In a first aspect, the invention is related to a catheter including a sheath having a distal-end region and a wire disposed within the sheath and attached to the distal end of the sheath. The wire has a distal-end region having a preformed shape with a radius of curvature. The wire is formed of a shape-retentive and resilient material such that the wire distal-end region changes shape upon the application of force and upon the removal of force, returns to the preformed shape. The wire is disposed in the sheath such that the wire distal-end region is located in the sheath distal-end and causes the sheath to assume the preformed shape. The catheter further includes an outer sleeve having a distal-end region having a distal end. The sleeve surrounds the sheath and is positioned relative thereto for movement between a retracted position and any of a plurality of advanced positions during which a portion of the sleeve distal-end region is coincident with a portion of the wire distal-end region. The sleeve is formed of a material having a stiffness sufficient to change the shape of the wire distal-end region. The catheter also includes a tendon housed within the sheath. The tendon is attached to the distal end of the sheath such that axial displacement of the tendon changes the radius of curvature of the portion of the wire distal-end region extending distal the distal end of the outer sleeve.
By providing a catheter having a preshaped steerable catheter sheath and a movable outer sleeve surrounding the sheath and having a stiffness sufficient to change the shape of the sheath, the present invention allows for multifaceted adjustment of the distal-end region shape such that intimate contact between the at least one electrode and the target tissue may be obtained regardless of the curvature of the biological site. For example, the preformed shape of distal-end region may be adjusted using the tendon or the movable outer sleeve or a combination of both.
In a more detailed facet of the invention, the outer sleeve has a fully advanced position during which the sleeve distal end is substantially coincident with the wire distal end. In another detailed facet, the outer sleeve has a fully retracted position during which the sleeve distal-end region is proximal the wire distal-end region. In yet another detailed aspect, the outer sleeve distal-end region comprises a preformed shape with a radius of curvature. In still another detailed aspect, the sheath has an axis and the outer sleeve is positioned for rotational movement about the axis of the sheath. In further detailed facets the catheter further includes a locking mechanism for locking the outer sleeve in a position relative to the sheath and a handle having the proximal end of the sheath and the wire connected thereto such that movement of the handle results in movement of the sheath, wire and outer sleeve. In a still another detailed aspect, the tendon is disposed in the sheath such that pulling the tendon in the proximal direction decreases the radius of curvature of the wire distal-end region distal the distal end of the sleeve and subsequent movement of the tendon in the distal direction allows an increase in the radius of curvature of the wire distal-end region distal the distal end of the sleeve.
In a second aspect, the invention is related to an ablation catheter for use in applying energy to heart tissue. The system includes a catheter sheath having a distal-end region, at least one electrode located at the sheath distal-end region and a wire disposed within the sheath and attached to the distal end of the catheter sheath. The wire has a distal-end region with a preformed shape with a radius of curvature and is formed of a shape-retentive and resilient material such that the wire distal-end region changes shape upon the application of force and upon the removal of the force, returns to the preformed shape. The wire is disposed in the catheter sheath such that the wire distal-end region is located in the distal-end region of the sheath and causes the sheath to assume the preformed shape.
The ablation catheter further includes an outer sleeve having a distal-end region having a distal end. The sleeve surrounds the sheath and is positioned relative thereto for movement between a retracted position and any of a plurality of advanced positions during which a portion of the sleeve distal-end region is coincident with a portion of the wire distal-end region. The sleeve is formed of a material having a stiffness sufficient to change the shape of the wire distal-end region. The system also includes a tendon housed within the sheath. The tendon is attached to the distal end of the sheath such that axial displacement of the tendon changes the radius of curvature of the portion of the wire distal-end region extending distal the distal end of the outer sleeve. The system further includes a locking mechanism for locking the outer sleeve in a position relative to the sheath and a handle attached to the proximal end of the catheter sheath and the wire such that movement of the handle causes movement of the catheter sheath, the wire and the outer sleeve.
In a third aspect, the invention involves a method for applying energy to biological tissue within a biological chamber of a patient. The method uses a catheter having a sheath having a distal end-region carrying a plurality of electrodes and a wire disposed within the sheath and attached to the distal end of the sheath. The wire has a distal-end region having a preformed shape with a radius of curvature and is formed of a shape-retentive and resilient material such that the wire distal-end region changes shape upon the application of force and upon the removal of force, returns to the preformed shape. The wire is disposed in the sheath such that the wire distal-end region is located in the sheath distal-end and causes the sheath to assume the preformed shape. The catheter also includes an outer sleeve having a distal-end region having a distal end. The sleeve surrounds the sheath and is positioned relative thereto for movement between a retracted position and any of a plurality of advanced positions during which a portion of the sleeve distal-end region is coincident with a portion of the wire distal-end region. The sleeve is formed of a material having a stiffness sufficient to change the shape of the wire distal-end region. The catheter also includes a tendon housed within the sheath and attached to the distal end of the sheath such that axial displacement of the tendon changes the radius of curvature of the portion of the wire distal-end region extending distal the distal end of the outer sleeve.
The method of the present invention includes the steps of placing the outer sleeve in an advanced position such that the distal end of the sheath is positioned within the outer sleeve, inserting the catheter into the vasculature of the patient and advancing the catheter into the biological chamber in which the selected tissue is located. The method also includes the steps of retracting the outer sleeve such that a portion of the distal-end region of the sheath is positioned outside of the outer sleeve thereby permitting the wire distal-end region to assume the preformed shape and advancing the distal-end region of the catheter sheath to a position proximal the selected biological tissue. The method further includes the step of adjusting the radius of curvature of the distal-end region of the wire to thereby affect adjustment in the distal-end region of the sheath such that a plurality of the electrodes contact the selected biological tissue.
In a detailed facet of the invention, the step of advancing the distal-end region of the catheter sheath to a position proximal the selected heart tissue includes the step of securing the outer sleeve to the sheath and axially displacing the catheter toward the selected biological tissue. In another detailed aspect, the step of advancing the distal-end region of the catheter sheath to a position proximal the selected heart tissue includes the step of maintaining the position of the outer sleeve while axially displacing the catheter sheath toward the selected biological tissue. In yet another detailed facet, the step of adjusting the radius of curvature of the distal-end region of the catheter includes the step of displacing the tendon to deflect the wire distal-end region and thereby decrease the curvature of the wire distal-end region.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.